Vertical stiffness of bicycle frame and its influence on rider comfort

Abstract

This study reports on relation between bicycle frame and rider comfort. It involves developing a theory on interdependence of vertical compliance or stiffness of bicycle frame and induced human comfort. The factors affecting vertical stiffness/compliance are identified and varied to observe their influence. A standard diamond type bicycle frame is modelled and analysed which is generally used for on-road bikes, applying different materials to the frame to note its deflection on application of load, considering the structural and material properties. The results of the analysis confirm with stiffness trend associated with Young's modulus of the material. i.e., for the same structure and loading conditions, material with lesser Young's modulus offer more compliance. Reducing thickness of tubing is also observed to be increasing compliance of the frame, which can be achieved either by reducing the outer diameter or increasing the inner diameter, the former being more beneficial according to manufacturing standpoint. This is verified by generating a series of supplementary equations. An experimental analysis is performed to discern the most influential tube out of every other tubings forming the frame structure, wherein their thicknesses are decreased by 10% one at a time, keeping the rest as it is. The study accomplishes that as compared to rest of the tubes, more rider comfort can be achieved by making least changes to the seat tube cross-sectional thickness, to decrease vertical stiffness and therefore, comfort. The obtained conclusions can serve as a base for further studies involving cyclist comfort and bicycle frame design.